The majority of pleasure boats currently utilize either outboard or stern drive propulsion systems that employ means to channel engine exhaust thru the propeller hub. See for example U.S. Pat. Nos. 4,875,829 and 4,802,872, for examples of constant pitch hubs having through the hub exhaust channels.
To improve the performance of these propulsion systems, designs have also been presented to provide means within the propeller hub to vary the pitch of the propeller blades, for example see U.S. Pat. Nos. 4,929,153 and 5,032,057. The mechanical components utilized in these variable pitch propellers generally result in a significant reduction in flow area available within the propeller hub that can be utilized for flow of the exhaust gases.
It is thus an object of the present invention to provide an increase in exhaust flow area. It is a further object of the present invention to provide a reduction in flow restriction while maintaining the variable pitch property and reducing engine exhaust back pressure.
In accordance with the present invention, a variable pitch marine propeller is provided having geometric arrangements that maintain the desirable low exhaust back pressure.